The present invention relates to an automatic clothes dryer and in particular to an electric control circuit for use during an automatic clothes drying cycle which provides ambient temperature compensation.
Clothes dryers are known to employ an operating thermostat responsive to the exhaust air temperature from the dryer to cycle the dryer heater on and off during the drying cycle to maintain the temperature in the dryer within a set range. Small heating elements may be placed adjacent the thermostat to provide a thermal bias. The provision of a thermal bias causes the thermostat to operate at a lower exhaust air temperature and is commonly used to lower the maximum exhaust air temperature at which the operating thermostat reacts.
While the use of thermally biased thermostats is known in the art, these thermostats have been used in automatic dryer applications where 240 volts is applied across the thermostats and dryer heater coils to deliver energy to heat the clothes to temperatures well above ambient. However, in small and mid-size clothes dryer applications where lower voltages of 110 to 120 volts and currents of 15 amps are employed, an automatic dryer operation has not been an energy efficient feature because the thermostats typically cause the dryer heating elements to automatically cycle on and off at too low of an outlet temperature. As a result, the dryers either have to apply heat to the clothing for periods longer than necessary or terminate the drying cycle when the clothes are still wet. This inefficient automatic drying operation problem is further enhanced when the ambient temperature around the dryer is relatively high resulting in a small temperature difference between the ambient temperature and the temperature at which the outlet dryer cycles on and off. As a result, automatic drying cycles have not been offered for all small and mid-sized dryers operating with 120 volt power sources. Instead, these dryers are provided with a time selected drying operation where the dryer operates at about 140xc2x0 F. for the time specified by the user before entering a cool down period.
Accordingly, there is a need for an energy efficient, ambient responsive, automatic dryer control circuitry suitable for use with small and mid-sized clothes dryers capable of operating with 120 volt power supply.
The present invention relates to a clothes dryer operating with a 120 volt power supply and having an automatic control circuit that compensates for changes in the ambient temperature to compensate for premature advancement of the dryer timer motor during an automatic drying cycle. The control circuit comprises a low outlet thermostat and a high outlet thermostat which control the energization of a heater in the dryer. The low outlet thermostat and the high outlet thermostat each open circuit at respective lower and higher predetermined temperatures when the outlet air flow from the dryer drum respectively reaches the lower or higher predetermined temperatures to thereby de-energize the heater and advance the timer motor. The control circuit includes an ambient thermostat that switches control of the heater energization and timer motor advancement from the low output thermostat to the high outlet thermostat when the ambient temperature rises above a predetermined ambient temperature. The control circuit provides for more energy efficient drying in an automatic drying cycle for small and mid-size dryers operating with a 120 volt power source.
The ambient thermostat preferably has an internal biasing heater or resistor that is energized to permit the ambient thermostat to switch between the low output thermostat and the high output thermostat when the predetermined ambient temperature is reached. Preferably, the internal biasing heater of the ambient thermostat is energized when the low output thermostat is open circuited.
In accordance with a further preferred aspect of the present invention, both the low and high output thermostats each have internal biasing heaters that are normally energized during the automatic drying cycle and are de-energized during time selected drying cycles so that the low and high temperature thermostats cycle on and off at higher temperatures than they would during the automatic drying cycle.
In accordance with an aspect of the present invention there is provided a control circuit for controlling the operation of a clothes dryer having a dryer drum, a drum air inlet and a drum air outlet permitting an air stream to flow into and out of the dryer drum, a heater for heating the air stream before the air stream passes into the dryer drum, and a control circuit for controlling energization of the heater during an automatic drying cycle.
The control circuit comprises:
a supply line and a neutral line adapted for connection to a 120 volt power supply source;
a series connection across the supply line and the neutral line of a low output temperature thermostat, a high output temperature thermostat and the heater, the low output temperature thermostat opening at a first predetermined temperature and the high output temperature thermostat opening at a second predetermined temperature higher than the first predetermined temperature thereby controlling energization of the heater;
a timer motor connected between the supply line and a first point located between the high output temperature thermostat and the heater, the timer motor advancing to end the automatic drying cycle during periods when either one of the low output temperature thermostat and high output temperature thermostat is open;
an ambient thermostat for sensing ambient temperature and being electrically connected in parallel with the low outlet thermostat and in series with the supply line and a second point between the low output temperature thermostat and the high output temperature thermostat, the ambient thermostat providing a bypass circuit around the low temperature thermostat when a predetermined ambient temperature is reached; and,
wherein, the low output temperature thermostat opens when the temperature of the air stream exiting out of the drum reaches the first predetermined temperature to control cycling on and off of the heater and to control the advancement of the timer motor, and wherein control cycling on and off of the heater and control of advancement of the timer motor in response to the high output temperature thermostat opening at the second predetermined temperature occurs when the first outlet thermostat is bypassed out of circuit by the ambient thermostat.